1. Field of the Invention
This invention relates to the monitoring of processing apparatus and more particularly to methods of and apparatus for monitoring for conditions indicative of incipient electrode or refractory wall failure in a heating and melting apparatus for Joule effect heated heat softenable material.
2. Description of the Prior Art
The electrical heating of heat softenable materials by Joule effect involves establishing electrical current communication with the material through electrodes. A typical heat softenable material, glass, has been maintained at or above the usual working temperatures, about 2600.degree.F, by immersing one or more pair of electrodes in the molten glass and passing controlled pulses of electrical power from the electrodes through the glass. Frequently these electrodes have substantial portions of their glass contacting surfaces spaced from the walls of the container or furnace for the glass to reduce the heat imposed on those walls and extend wall life. One electrode form involves a right circular cylinder which is extended through the bottom of the furnace. Although a number of expedients are employed to protect the electrode and the bottom refractory, it has been found that there is a tendency for electrodes to erode in the vicinity of the wall through which they pass.
In the case of the cylindrical electrodes cooling jackets have been mounted around the electrodes, beneath the furnace bottom to reduce the electrode temperature external of the furnace to a level at which it is not subject to attack by constituents of the atmosphere. Further, it is not uncommon to maintain an inert atmosphere within the jacket and around the electrode so it is protected in the portion of its length in which the temperature approaches that within the furnace. Even with such precautions electrodes tend to erode, usually in the vicinity of and slightly below the furnace floor-molten glass interface. Such erosion can result in the breaking off of the electrode in the melt.
Upon breaking an electrode, the furnace wall in the vicinity of the remaining stub portion is attacked and will develop leaks unless corrective action is taken promptly.